source: src/main/java/com/example/rezevirajmasa/demo/config/UserAuthProvider.java

package com.example.rezevirajmasa.demo.config;

import com.auth0.jwt.JWT;
import com.auth0.jwt.JWTVerifier;
import com.auth0.jwt.algorithms.Algorithm;
import com.auth0.jwt.interfaces.DecodedJWT;
import com.example.rezevirajmasa.demo.dto.UserDto;
import com.example.rezevirajmasa.demo.service.UserService;
import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jwts;
import jakarta.annotation.PostConstruct;
import lombok.RequiredArgsConstructor;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.stereotype.Component;

import java.util.*;
import java.util.function.Function;

@RequiredArgsConstructor
@Component
public class UserAuthProvider {
    @Value("${security.jwt.token.secret-key:secret:value}")
    private String secretKey;

    private final UserService userService;

    @PostConstruct
    protected void init() {
        secretKey = Base64.getEncoder().encodeToString(secretKey.getBytes());
    }

    public String generateToken(UserDetails userDetails){
        Map<String, Object> claims = new HashMap<>();
        return createToken(userDetails.getUsername());
    }

    public String createToken(String login) {
        Date now = new Date();
        Date validity = new Date(now.getTime() + 3_600_000);
        return JWT.create()
                .withIssuer(login)
                .withIssuedAt(now)
                .withExpiresAt(validity)
                .sign(Algorithm.HMAC256(secretKey));
    }

    public Authentication validateToken(String token) {
        JWTVerifier verifier = JWT.require(Algorithm.HMAC256(secretKey)).build();

        DecodedJWT decoded = verifier.verify(token);

        UserDto user = userService.findByEmail(decoded.getIssuer());

        return new UsernamePasswordAuthenticationToken(user, null, Collections.emptyList());
    }

    public String extractUsername(String token) {
        return extractClaim(token, Claims::getSubject);
    }

    public Date extractExpiration(String token) {
        return extractClaim(token, Claims::getExpiration);
    }

    public <T> T extractClaim(String token, Function<Claims, T> claimsResolver) {
        final Claims claims = extractAllClaims(token);
        return claimsResolver.apply(claims);
    }

    private Claims extractAllClaims(String token) {
        return Jwts.parser().setSigningKey(secretKey).parseClaimsJws(token).getBody();
    }

    private Boolean isTokenExpired(String token) {
        return extractExpiration(token).before(new Date());
    }
}